Dayside ionospheric response to recurrent geomagnetic activity during the extreme solar minimum of 2008

Abstract. In this paper we use wavelets and Lomb–Scargle spectral analysis techniques to investigate the changing pattern of the different harmonics of the 27-day solar rotation period of the AE (auroral electrojet) index during various phases of different solar cycles between 1960 and 2014. Previous investigations have revealed that the solar minimum of cycles 23–24 exhibited strong 13.5- and 9.0-day recurrence in geomagnetic data in comparison to the usual dominant 27.0-day synodic solar rotation period. Daily mean AE indices are utilized to show how several harmonics of the 27-day recurrent period change during every solar cycle subject to a 95 % confidence rule by performing a wavelet analysis of each individual year's AE indices. Results show that particularly during the solar minimum of 23–24 during 2008 the 27-day period is no longer detectable above the 95 % confidence level. During this interval geomagnetic activity is now dominated by the second (13.5-day) and third (9.0-day) harmonics. A Pearson correlation analysis between AE and various spherical harmonic coefficients describing the solar magnetic field during each Carrington rotation period confirms that the solar dynamo has been dominated by an unusual combination of sectorial harmonic structure during 23–24, which can be responsible for the observed anomalously low solar activity. These findings clearly show that, during the unusual low-activity interval of 2008, auroral geomagnetic activity was predominantly driven by high-speed solar wind streams originating from multiple low-latitude coronal holes distributed at regular solar longitude intervals.

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Extremely low geomagnetic activity during the recent deep solar cycle minimum

Proceedings of the International Astronomical Union ◽

10.1017/s174392131200484x ◽

2011 ◽

Vol 7 (S286) ◽

pp. 200-209 ◽

Cited By ~ 12

Author(s):

E. Echer ◽

B. T. Tsurutani ◽

W. D. Gonzalez

Keyword(s):

Solar Wind ◽

Solar Cycle ◽

Geomagnetic Activity ◽

Solar Minimum ◽

Solar Wind Speed ◽

Sunspot Cycle ◽

Cycle Minimum ◽

Current Minimum ◽

Solar Wind Parameters ◽

Xix Century

AbstractThe recent solar minimum (2008-2009) was extreme in several aspects: the sunspot number, Rz, interplanetary magnetic field (IMF) magnitude Bo and solar wind speed Vsw were the lowest during the space era. Furthermore, the variance of the IMF southward Bz component was low. As a consequence of these exceedingly low solar wind parameters, there was a minimum in the energy transfer from solar wind to the magnetosphere, and the geomagnetic activity ap index reached extremely low levels. The minimum in geomagnetic activity was delayed in relation to sunspot cycle minimum. We compare the solar wind and geomagnetic activity observed in this recent minimum with previous solar cycle values during the space era (1964-2010). Moreover, the geomagnetic activity conditions during the current minimum are compared with long term variability during the period of available geomagnetic observations. The extremely low geomagnetic activity observed in this solar minimum was previously recorded only at the end of XIX century and at the beginning of the XX century, and this might be related to the Gleissberg (80-100 years) solar cycle.

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Spatial and seasonal effects on the delayed ionospheric response to solar EUV changes

10.5194/angeo-2019-91 ◽

2019 ◽

Author(s):

Erik Schmölter ◽

Jens Berdermann ◽

Norbert Jakowski ◽

Christoph Jacobi

Keyword(s):

Southern Hemisphere ◽

Geomagnetic Activity ◽

Correlation Coefficients ◽

Seasonal Effects ◽

Constant Delay ◽

Average Delay ◽

Ionospheric Response ◽

The Difference ◽

Longitudinal Variability ◽

The Impact

Abstract. This study correlates different ionospheric parameters with the integrated solar EUV radiation for an analysis of the delayed ionospheric response in order to confirm previous studies on the delay and to further specify variations of the delay. Several time series for correlation coefficients and delays are presented to characterize the trend of the delay from 2011 to 2013. The impact of the diurnal variations of ionospheric parameters in the analysis on hourly resolution for fixed locations are discussed and specified with calculations in different time scales and with comparison to solar and geomagnetic activity. An average delay for TEC of &approx; 18.7 hours and for foF2 of &approx; 18.6 hours is calculated at four European stations. Through comparison with the Australian region the difference between northern and southern hemisphere is analyzed and a seasonal variation of the delay between northern and southern hemisphere is calculated for TEC with &approx; 5 ± 0.7 hours and foF2 with &approx; 8 ± 0.8 hours. The latitudinal and longitudinal variability of the delay is analyzed for the European region and a decrease of the delay from &approx; 21.5 hours at 30° N to &approx; 19.0 hours at 70° N has been found. For winter months a roughly constant delay of &approx; 19.5 hours is calculated. In this study a North-South trend of the ionospheric delay during summer month has been observed with &approx; 0.06 hours per degree in latitude. The results based on solar and ionospheric data in hourly resolution and the analysis of the delayed ionospheric response to solar EUV show the seasonal and latitudinal variations. Results also indicate the dependence on the geomagnetic activity as well as on the 11-year solar cycle.

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The Two‐Dimensional Evolution of Thermospheric ∑O/N 2 Response to Weak Geomagnetic Activity During Solar‐Minimum Observed by GOLD

Geophysical Research Letters ◽

10.1029/2020gl088838 ◽

2020 ◽

Vol 47 (18) ◽

Cited By ~ 1

Author(s):

Xuguang Cai ◽

Alan G. Burns ◽

Wenbin Wang ◽

Liying Qian ◽

Stanley C. Solomon ◽

...

Keyword(s):

Geomagnetic Activity ◽

Solar Minimum ◽

Two Dimensional

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Investigating the foF2 variations at the Ionospheric Observatory of Rome during different solar cycles minimums and levels of geomagnetic activity

Journal of Space Weather and Space Climate ◽

10.1051/swsc/2020054 ◽

2020 ◽

Vol 10 ◽

pp. 52

Author(s):

Alessandro Ippolito ◽

Loredana Perrone ◽

Christina Plainaki ◽

Claudio Cesaroni

Keyword(s):

Geomagnetic Activity ◽

Solar Minimum ◽

Critical Frequency ◽

Background Level ◽

Solar Cycles ◽

Physical Processes ◽

Minimum Duration ◽

Critical Frequency Fof2 ◽

Definition Of ◽

Low Activity

The variations of the hourly observations of the critical frequency foF2, recorded at the Ionospheric Observatory of Rome by the AIS-INGV ionosonde (geographic coordinates 41.82° N, 12.51° E; geomagnetic coordinates 41.69° N, 93.97° E) during the low activity periods at the turn of solar cycles 21–22, 22–23 and 23–24, are investigated. Deviations of foF2 greater than ± 15% with respect to a background level, and with a minimum duration of 3 h, are here considered anomalous. The dependence of these foF2 anomalies on geomagnetic activity has been accurately investigated. Particular attention has been paid to the last deep solar minimum 2007–2009, in comparison with the previous solar cycle minima. The lack of day-time anomalous negative variations in the critical frequency of the F2 layer, is one of the main findings of this work. Moreover, the analysis of the observed foF2 anomalies confirms the existence of two types of positive F2 layer disturbances, characterised by different morphologies and, different underlying physical processes. A detailed analysis of four specific cases allows the definition of possible scenarios for the explanation of the mechanisms behind the generation of the foF2 anomalies.

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An alternative way to identify local geomagnetically quiet days: a case study using wavelet analysis

Annales Geophysicae ◽

10.5194/angeo-34-451-2016 ◽

2016 ◽

Vol 34 (4) ◽

pp. 451-462 ◽

Cited By ~ 4

Author(s):

Virginia Klausner ◽

Andrés Reinaldo Rodriguez Papa ◽

Cláudia Maria Nicole Cândido ◽

Margarete Oliveira Domingues ◽

Odim Mendes

Keyword(s):

Wavelet Analysis ◽

Geomagnetic Activity ◽

Solar Minimum ◽

High Speed ◽

Wavelet Coefficient ◽

Magnetic Activity ◽

New Method ◽

Storm Events ◽

High Speed Stream

Abstract. This paper proposes a new method to evaluate geomagnetic activity based on wavelet analysis during the solar minimum activity (2007). In order to accomplish this task, a newly developed algorithm called effectiveness wavelet coefficient (EWC) was applied. Furthermore, a comparison between the 5 geomagnetically quiet days determined by the Kp-based method and by wavelet-based method was performed. This paper provides a new insight since the geomagnetic activity indexes are mostly designed to quantify the extent of disturbance rather than the quietness. The results suggest that the EWC can be used as an alternative tool to accurately detect quiet days, and consequently, it can also be used as an alternative to determine the Sq baseline to the current Kp-based 5 quietest days method. Another important aspect of this paper is that most of the quietest local wavelet candidate days occurred in an interval 2 days prior to the high-speed-stream-driven storm events. In other words, the EWC algorithm may potentially be used to detect the quietest magnetic activity that tends to occur just before the arrival of high-speed-stream-driven storms.

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